OBJECTIVE: To identify the mechanisms which mediate suppression of the stress hormone cortisol in socially subordinate, reproductively suppressed female marmosets. RESULTS Chronic dysfunction of the stress-responsive hypothalamo-pituitary-adrenal endocrine axis, manifest as elevated or suppressed plasma cortisol levels, is often associated with neuropsychiatric disorders in humans. As a possible model for these endocrine disturbances, we have been investigating the causes of chronic cortisol suppression in socially subordinate, reproductively suppressed female marmosets. To date, we have examined (1) baseline adrenocorticotrophic hormone (ACTH) levels, to determine whether cortisol suppression is caused by reduced pituitary stimulation of the adrenal cortex; (2) ACTH and cortisol responses to dexamethasone, a synthetic glucocorticoid, to determine whether subordinate females exhibit enhanced sensitivity to glucocorticoid negative feedback; and (3) cortisol responses to exogenous ACTH, to determine whether cortisol suppression is associated with reduced adrenal sensitivity. Results thus far indicate that neither baseline plasma ACTH levels nor the pituitary and adrenocortical responses to dexamethasone differ between groups. However, anovulatory subordinate females appear to show a blunted adrenocortical response to exogenous ACTH. These results suggest that reduced adrenocortical responsiveness might be an important component of adrenocortical suppression in subordinate females. FUTURE DIRECTIONS We will continue to investigate the roles of the brain, pituitary, and adrenal cortex in mediating socially induced suppression of cortisol, and to develop the subordinate female marmoset as a possible model of cortisol dysregulation in human neuropsychiatric disorders, such as post-traumatic stress disorder. KEY WORDS Dominance, subordination, ovarian cycle, adrenal cortex, adrenocorticotrophic hormone, glucocorticoids